Offsetting of Assets and Liabilities (Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell) (Detail) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	$ 2,423.3	$ 1,791.3
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	2,179.8	1,779.2
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	243.5	12.1
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	10.2	2.7
NET AMOUNT	233.3	9.4
Total Derivatives Not Subject to a Master Netting Arrangement
Total Derivatives Not Subject to a Master Netting Arrangement	1,434.4	303.0
Total Derivatives
GROSS RECOGNIZED ASSETS	3,857.7	2,094.3
Derivative Assets	1,677.9	315.1
NET AMOUNT	1,667.7	312.4
Securities Purchased under Agreements to Resell
GROSS RECOGNIZED ASSETS	98,862.1	92,669.7
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	97,183.2	90,015.6
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	1,678.9	2,654.1
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	1,678.9	2,654.1
NET AMOUNT	0.0	0.0
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	2,332.0	1,707.2
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	2,088.5	1,696.1
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	243.5	11.1
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	10.2	2.7
NET AMOUNT	233.3	8.4
Interest Rate Swap Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	91.3	83.4
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	91.3	82.4
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	0.0	1.0
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.0	0.0
NET AMOUNT	$ 0.0	1.0
Interest Rate Swap Contracts | Interest Rate Swaps Exchange Cleared
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS		0.7
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET		0.7
NET AMOUNTS PRESENTED IN THE BALANCE SHEET		0.0
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET		0.0
NET AMOUNT		$ 0.0